Combining Organic and Inorganic Solar Cells to Achieve Power Conversion Efficiencies > 20%

There is a need for photovoltaic technologies with power conversion efficiencies (PCEs) exceeding 20% that can be produced with a module cost under $0.50 per Watt. We believe that making hybrid tandems with organic solar cells on top of silicon or CIGS solar cells is one of the most promising approaches to meeting this need.
Organic photovoltaics have a significant processing advantage over inorganic alternatives for the top cell in a tandem because they can be easily deposited by solution processing techniques at or near room temperature without damaging the bottom cell. Furthermore, the cost of the organic layers themselves has been estimated to be less than $10/m2, so that they can be added to a variety of commercial inorganic cells with little addition cost.
We have modeled hybrid tandems and found that organic photovoltaics are just starting to have the performance that is required to improve silicon or CIGS solar cells. Within a few years we believe that hybrid tandems could be 20 to 35 % more efficient than the bottom cells by themselves.
The key challenges to making this approach commercially viable will be increasing the voltage of organic solar cells while maintaining an internal quantum efficiency > 90 %, depositing high-quality transparent electrodes without damaging the organic semiconductors and obtaining > 20-year lifetime.
We study the fundamental electronic and chemical processes that occur in organic photovoltaics and will present our thoughts on how to obtain the desired efficiency and lifetime. We will also show that we can spray transparent electrodes based on silver nanowires that outperform conventional electrodes based on indium tin oxide.

Speaker: Mike McGehee, Stanford University

Room 390